There are indeed many applications for use of a device such as an electronic probe fluid level sensor. Some of the more obvious applications include the measurement of the oil level within an internal combustion engine, a measurement of the fuel level for an engine or other fuel consumption device or the level of fluid in the bilges of an ocean going vessel or the like. The sensor could be used to determine the level of a critical fluid within a process thus assuring a predictable result.
The oil level within an internal combustion engine is usually determined by means of a dipstick or the like requiring the operator or attendant to have access to the engine, a requirement which is at best inconvenient and in some operations such as large construction vehicles, boats or the like virtually impossible without machine downtime.
Attempts have been made to automate the liquid level sensing and prior art noted in a novelty search illustrative of early attempts include U.S. Pat. No. 2,134,104 granted to Cressy on Oct. 25, 1938 which discloses a liquid level indicator including a float mechanically connected to a magnetic armature which moves within a reactance coil to proportionately reflect the location of the float ball and thus the liquid level within a closed tank.
U.S. Pat. No. 2,337,608 granted Hurlsberg on Dec. 28, 1943 discloses a liquid level sensing mechanism wherein mechanical means are utilized to move an inductive coil interconnected with an alternating current along the outside of an elongated float chamber in search of a mass of iron supported by a captured float. The iron alters the impedance of a coil and thus deflects the reading of a meter responsive to the alternating current. Such an apparatus by both its principal of operation and its physical configuration is limited in application to structures or installations where there is ample space and cannot be used in conjunction with a small diameter probe.
U.S. Pat. No. 2,804,517 granted Aug. 27, 1957 to Ferry indicates an oil level indicator incorporated in a probe type mechanism. The reference includes the utilization of a float having a conductive surface such that when the fluid level reaches a critical stage the conductive float will complete the circuit between the conductive tubular containment device and ground thus lighting an indicator lamp.
U.S. Pat. No. 2,853,878 granted to Anderson et al on Sept. 30, 1958 discloses yet another electronic means for measuring fluid. A float of magnetic material is used in conjunction with a series of vertically placed and spaced magnetometers to detect the position of a float in a step-by-step manner. Because of the generation of a magnetic flux field, this device necessarily requires a substantial amount of space for the detecting device as well as an AC current for the energization or generation of the flux.
U.S. Pat. No. 3,389,603 granted to Jacobs III on June 25, 1968 includes a float device having a magnetic element embedded therein. The magnet is of a sufficient strength to energize a reed switch secured adjacent the sight glass containing the magnet thus giving an indication of the liquid level.
U.S. Pat. No. 3,820,396 granted to Gamer et al on June 28, 1974 discloses a fluid level indicator wherein a buoyant movable element is placed within a transparent guide tube. The indicator sets up an RF or high potential field inside the tube which causes a gas captured within the movable element to glow when the element is within the field, thus giving a visual indication of the liquid level.
U.S. Pat. No. 3,895,235 granted to Melone on July 15, 1975 discloses a liquid level and specific gravity indicator wherein a light beam is transmitted downwardly through the fluid and reflected back through another path. If the liquid is below a certain level, a floating ball acts as a shutter to block light between the prisms, interrupting the beam and thus indicating the level within the container.
U.S. Pat. No. 3,968,687 granted to Fester on July 13, 1976 discloses a device for indicating a specific gravity and/or level of an electrolyte within a wet storage battery. The device includes a magnetically actuated switch secured to the battery and a floatation device which responds both to the level of the electrolyte and the specific gravity of electrolyte. The floatation device actuates the switch if either the level or the specific gravity of the fluid drops below a predetermined level.
French Pat. No. 820,993 granted to Pautou on July 28, 1936 discloses a liquid level sensing mechanism in which the impedance of an alternating current coil with variably spaced windings encased in a cylindrical chamber is altered by the presence of a soft iron float. It would appear from the circuit and the elements involved in the circuit that it would take a fairly large mass of metal to alter the position of the needle thus restricting this structure to installations of fairly large size.
As can readily be seen, the prior art, while addressing the problem of electronically sensing the fluid level within a closed or remote container, does not address the problem of sensing same with a device which is readily adaptable to varying environments and needs. The advantages of a probe like device are many fold. For example, a standard automobile engine including a dipstick for determining the oil level could easily incorporate an electronic probe in accordance with the present invention without any restructuring of the engine. In engines yet to be built, an electronic probe could be incorporated as a part of the engine and will more accurately reflect engine conditions than is presently possible without occupying a great deal of space within the engine and thus necessitating redesign.
Another advantage of the electronic probe as hereinafter disclosed lies in the fact that it is essentially unaffected by a hostile environment and can withstand both high temperatures and corrosive fluids.
A further advantage of the present mechanism, when electrically interconnected to a warning light or other such system, is that it will generate a negative response, i.e., indicate insufficient fluid or a condition needing attention in the case of any malfunction of the probe or the interconnecting electronics.
Still a further advantage of the present invention lies in the fact that the probe and the circuitry necessary to activate a display or the like, are extremely compact and light in weight. The compactness makes the device easily usable within the space available within a vehicle, within its engine or the operator's station. The low weight is an advantage for aircraft applications.
Yet another distinct advantage of the present invention lies in the fact that the inventive sensing device is extremely accurate and further since the sensing circuit is in a balanced condition, a slight change in the efficiency of the coil due to the introduction of the float immediately causes a significant change in amplitude of the oscillator signal.
With the above noted advantages in mind, it is an object of the present invention to provide an electronic probe type fluid sensor wherein the sensor is extremely compact and capable of being inserted into the bore or opening normally utilized for a fluid indicating dipstick in vehicles.
It is another object of the present invention to provide an electronic fluid level probe wherein the construction and circuitry is such that any malfunction whether it be liquid below a certain level or a short in the circuit would initiate an "attention required" signal.
It is still a further object of the present invention to provide a fluid level sensor which in its preferred embodiment is designed for use in automobiles wherein a fluid level indicating dipstick is replaced by a hollow probe having mounted therein a sensing mechanism electrically interconnected with a warning light or other indicator on the dash indicating a condition requiring attention.
Still a further object of the present invention is to provide an electronic probe requiring very little space and one wherein the level of the fluid is indicated by utilization of a small buoyant object which is captured and restricted to a path of movement axially of a wound coil of small diameter. The object moves into or out of the coil depending upon the fluid depth.
Yet another object of the present invention is to provide a liquid level indicator which is directly responsive to the level since the level is reflected by a metallic buoyant ball captured and restricted in path of movement to assure detection.
Still a further object of the present invention is to provide an electronic probe fluid level detector which may be used in conjunction with other detectors thereby yielding a step-by-step level indication.
Yet a further object of the present invention is to provide a fluid detection device utilizing a coil as an integral part of an oscillator circuit wherein portions of the coil may be used as inputs for a second or tertiary oscillating circuit thereby rendering the primary coil self-calibrating.
Another object of the present invention is to provide a main coil having a float mounted therein for detection of fluid level and having a secondary or tertiary coil coaxial with the main coil and serving as the input for a second oscillator circuit such that the float passing through the coaxial coils can, in fact, give two separate and distinct outputs simultaneously.